Wide band gap semiconductors are materials having a high breakdown voltage and are thus often used as solid state switches for high-temperature and power switching applications involving large electric fields. While the exact threshold of what bandgap range is considered “wide” often depends on the application, wide bandgap semiconductor materials are generally considered to be those having bandgaps greater than about 1.6 or 1.7 eV. Furthermore, such wide bandgap materials are known to be photoconductive, i.e. characterized by increased electrical conductivity in response to illumination. Example types of include, silicon carbide, aluminum nitride, gallium nitride, boron nitride, and diamond. In particular, both gallium nitride and silicon carbide are well known robust materials well suited for such switching applications.
Various pulsed power applications are known which employ such photoconductive wide bandgap semiconductor materials (hereinafter “PWBSM”) as photoconductive solid state switches (PCS). Typical materials for a PCS are Si or GaAs, but because of the limited photocurrent current capacity, require operation in an avalanche or so called high-gain mode to generate usable energy levels. In avalanche mode operation, the device is bi-stable (i.e., either “off” or “on”) and is triggered “on” optically and stays “locked-on” until current cessation.
One example application using pulsed power is in the field of high power microwave generation, where such photoconductive materials are also used as photoconductive solid state switches. However, because they are operated in avalanche mode this produces broadband, low radiated energy, is not real-time-adaptive, and can cause communication fratricide. Spectral energy content is low because efficient energy radiation occurs mainly during the pulse transition. It is notable that traditionally, high-power microwave sources have been vacuum electronic devices, such as klystrons. Alternate approaches include nonlinear transmission lines. Both of these techniques have inherent problems. Vacuum electronic devices tend to be bulky and expensive, while nonlinear transmission lines rely on specialized materials which are often difficult to obtain and poorly characterized.